The invention relates to a process for the preparation of middle distillates from one or more mono-olefins having at most five carbon atoms per molecule (for the sake of brevity hereinafter referred to as "C.sub.5.sup.- -olefins") or from aliphatic hydrocarbon mixtures consisting more than 50%w of C.sub.5.sup.- -olefins by using a catalyst comprising a crystalline metal silicate of a special structure.
C.sub.5.sup.- -olefins and aliphatic hydrocarbon mixtures consisting more than 50%w of C.sub.5.sup.- -olefins can be converted in high yields into aromatic hydrocarbon mixtures by contacting them at a temperature above 400.degree. C. with a catalyst comprising a crystalline metal silicate of a special structure. Said crystalline metal silicates are characterized in that after one hour's calcination in air at 500.degree. C. they have the following properties:
(a) an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A,
TABLE A ______________________________________ d(.ANG.) ______________________________________ 11.1 .+-. 0.2 10.0 .+-. 0.2 3.84 .+-. 0.07 3.72 .+-. 0.06; and ______________________________________
(b) in addition to SiO.sub.2, one or more oxides of a trivalent metal A chosen from aluminum, iron, gallium, rhodium, chromium and scandium are present, and in which the SiO.sub.2 /A.sub.2 O.sub.3 molar ratio is higher than 10.
The hydrocarbon mixtures thus obtained consist substantially of components boiling in the gasoline range and contain only few components boiling in the middle distillate range. Consequently the abovementioned conversion of olefins is an unattractive route for the preparation of middle distillates on a technical scale.
As examples of prior art processes, U.S. Pat. No. 4,211,640 discloses a process whereby a gasoline having a olefinic content of at least 50%wt is converted into a product comprising both fuel oil and gasoline with enhanced gum stability over a H.sup..+-. ZSM-5 catalyst at a temperature of 177.degree.-316.degree. C. Also, U.S. Pat. No. 4,227,992 converts C.sub.3 -C.sub.5 olefins, which are present in a C.sub.2 -C.sub.5 olefin mixture, into a product comprising both fuel oil and gasoline over a H.sup..+-. ZSM-5 catalyst at a temperature of 149.degree.-316.degree. C. In addition, U.S. Pat. No. 3,845,150 describes the preparation of aromatic gasoline from lower olefins at a temperature of 343.degree.-816.degree. C. over ZSM-5, which may contain metals such as rare earth, magnesium, zinc, calcium, nickel and mixtures thereof.
In this patent application "middle distillates" should be taken to be hydrocarbon mixtures whose boiling range corresponds subtantially with that of the kerosene and gas oil fractions obtained in the conventional atmospheric distillation of crude mineral oil. During said distillation, from the crude mineral oil are separated in succession: one or more gasoline fractions having a boiling range between 30.degree. and 200.degree. C., one or more kerosene fractions having a boiling range between 140.degree. and 300.degree. C. and one or more gasoil fractions having a boiling range between 180.degree. and 370.degree. C.
It has been found that C.sub.5.sup.- -olefins and aliphatic hydrocarbon mixtures consisting more than 50%w of C.sub.5.sup.- -olefins can be converted in high yields into a hydrocarbon mixture a considerable part of which consists of components boiling in the middle distillate range by contacting the feed at a temperature between 150.degree. and 300.degree. C. with a crystalline metal silicate having the properties mentioned hereinbefore under (a) and (b) above, which metal silicate comprises at least 0.1%w nickel and/or cobalt deposited thereon by means of ion exchange. The principle underlying the present invention is a combination of the use of a low reaction temperature with the use of a crystalline metal silicate upon which nickel and/or cobalt has been deposited by ion exchange. Only if both these requirements are met will a product be obtained a considerable part of which consists of components boiling in the middle distillates range. Neither of these measures alone--for instance using a low reaction temperature, but combined with the use of a crystalline metal silicate onto which nickel or cobalt has been deposited by impregnation, or using a crystalline metal silicate onto which nickel or cobalt has been deposited by ion exchange, but combined with the use of a high reaction temperature--will produce the desired results.